Loss of the ability to transform present experience to what can be later remembered is one of the most dreaded afflictions of the human condition. It is present in various neurological disorders including temporal lobe epilepsy, traumatic brain injury and other hippocampal injuries such as those occurring during stroke, cardiac arrest, or encephalitis. It is also one of the first features of Alzheimer's Disease (AD) which affects millios of people in the US and worldwide, and is an unwelcome companion of the aging process becoming an increased burden on individual and society. Decades of research have established that declarative memory, the ability to remember recently experienced facts and events, depends on the hippocampus and associated structures in the medial temporal lobe (MTL), including the entorhinal cortex. In particular, understanding the role of the hippocampus and its relationship to afferent input from the entorhinal cortex is of considerable significance, as insul to this connective circuitry is very early and disproportionally affected in temporal lobe epilepsy AD and other neurological disorders, resulting in profound effects on memory. The applicant's laboratory has been the leader in single neuron physiology of the human MTL and recently published findings in the New England Journal of Medicine showing dramatic spatial memory enhancement when deep brain stimulation (DBS) of the human entorhinal area was given during the learning phase [13]. The present project will characterize the mechanisms of DBS through simultaneous recording of single neuron and local field potentials (LFPs). The project utilizes a rare opportunity to record the activity of single neurons and LFPs from depth electrodes implanted in patients with intractable epilepsy in order to identify the seizure focus fr potential surgical cure. A primary objective is to characterize the effect of DBS on learning vs. recall phases of memory, including both spatial and non-spatial memory, in addition to understanding its longitudinal effects. The project will elucidate the complex relationship between single neuronal responses, LFP oscillations, and DBS that underlies memory enhancement. Lastly the project will investigate variations in memory enhancement associated with changes in electrode placement through the use of high-resolution magnetic resonance imaging and high-resolution diffusion tensor imaging. By these three lines of investigation the project will develop insight into the mechanisms of memory enhancement associated with DBS in humans, contribute to the understanding of the MTL and its role in memory, and ultimately provide novel therapeutic approaches to human memory disorders.